I think the reason po boxes are not allowed is to clamp down on terrorism and fraud (people hiding their identity). Since terrorism and fraud are probably here to stay for our lifetimes at least, the demand for what you propose should continue. In other words I don’t think the gov’t will provide us with a solution.
It’s an interesting idea. I wonder what laws might interfere, say if your operation was investigated. I’m guessing the units would have to be habitable. There could be one bathroom and shower that is shared, which could actually be used by your staff.
$150/month is $18,000 after 10 years. You could sell them for $25,000 or rent them by the month or year. Just as people take roommates to split the rent, maybe 6 people could squeeze into those units(?). That would be 1/6th of $18,000, or $3,000 for 10 years. This I would consider.
But I wonder if there is a law to block this. I know of many cases where 10-15 people live in one unit, and I’ve never heard there was a problem with it legally. At least it wasn’t enforced.
If you found a low tax area with zoning that permits a business and residences on the same or adjacent lots, you could use your staff to run a copy & mail center too.
Maybe once you set this up it could run itself.